Heating device operated with liquid fuel

ABSTRACT

In a heating device operated with liquid fuel, comprising a fuel pump ( 1 ) which includes a displacer member ( 2 ) and serves to suck the liquid fuel out of a tank ( 6 ) and feed it to a pressure conduit region ( 7, 9 ) in which an increased pressure defined by a pressure regulator ( 14 ) prevails and which further passes the fuel to an atomizer nozzle ( 10 ) from which it passes into a combustion chamber to form a burner flame ( 11 ), to avoid interruptions in operation it is provided that the pressure conduit region ( 7, 9 ) includes at least one additional volume ( 20, 22; 24, 26 ), the size of which is so selected that the pressure drop occurring in the pressure conduit region ( 7, 9 ) when gas bubbles are sucked in does not lead to an ongoing interruption in the fuel delivery by the fuel pump ( 1 ).

The invention concerns a heating device operated with liquid fuel of the kind set forth in the classifying portion of claim 1 and a fuel pump suitable for such a heating device.

Hereinafter the term “conduit” is used to denote all kinds of hollow spaces and hollow bodies which are capable of serving as a flow path for a fluid, in particular a liquid, and which for that purpose have at least one feed opening and at least one outlet opening. Besides pipe conduits these also include for example through bores in solid bodies of any external shape, passages which with the exception of feed and outlet openings are closed on all sides, and so forth. The expression “conduit region” is used to denote a plurality of such conduits which are or can be connected together in flow relationship and which can also be connected to one or more bores or recesses which are of a blind hole-like configuration, namely having only one connecting opening, which are adapted to receive and store a fluid, in particular a liquid.

The heating devices involved herein are used either in the form of heating appliances or heating systems which are installed in private motor vehicles, buses, railway vehicles and like, and which serve for heating the interior compartments of those vehicles or however also for preheating the radiator water for example of diesel engines, or they are in the form of stationarily installed heating plants for example for heating buildings.

They include a fuel pump, by means of which the fluid fuel is sucked in from a supply container or tank and fed to a pressure conduit region in which an increased pressure defined by a pressure regulator or pressure limiter prevails and from which the fuel flows to an atomizer nozzle, through which it is injected into a burner chamber to form a burner flame.

Frequently there is provided a shut-off device which for example can be in the form of a solenoid shut-off valve and can be closed to interrupt the feed of fuel to the atomizer nozzle.

Particularly in the case of heating devices which include a blower driven jointly with the fuel pump a distinction can be drawn between three typical operating phases, the common factor of which is that the fuel pump runs and conveys fuel from the tank into the pressure conduit region:

-   -   a) Run-Up Mode of Operation     -   This operating phase in which the shut-down device is closed so         that no fuel can pass to or issue from the atomizer nozzle         serves to build up the required operating pressure in the         pressure conduit region. An excessively conveyed amount of fuel         which the pressure conduit region can no longer accommodate is         returned to the tank by means of the pressure regulator by way         of a return conduit branching off the pressure conduit region.     -   b) Heating Mode of Operation     -   The shut-off device is opened, fuel issues from the atomizer         nozzle and the flame serving for heating is formed after         ignition has occurred in the burner chamber. So that the         pressure regulator is capable of maintaining the increased         operating pressure in the pressure conduit region         “over-conveying” generally has to take place, that is to say the         pump in the heating mode must feed the pressure conduit region         with more fuel than issues through the atomizer nozzle. The         excess fuel flows back to the tank by way of the return conduit.     -   c) Shut-Down Mode of Operation     -   In this operating phase the shut-down device is closed again, no         fuel issues from the atomizer nozzle and the flame is         extinguished. For cooling purposes however the blower and         therewith the fuel pump continue to run. The conveyed fuel flows         back to the tank by way of the return conduit.

The level of the suction-side reduced pressure produced by the fuel pump is dependent on numerous factors like for example the components in the suction conduit (including the fuel filter), the length of the suction conduit, the speed of rotation of the pump, the viscosity of the conveyed fuel, that varies with temperature, and so forth.

Gas bubbles of widely differing sizes can occur in the fuel conveyed in the suction intake system because, when the reduced pressure reaches certain values, vaporization of the fuel occurs and/or because the fuel system may have leaks leading to the intake of air bubbles and/or because gas bubbles formed in the supply tank are also sucked in.

If the gaseous constituents make up a given proportion of the total volume delivered by the pump, then in conjunction with the pressure regulator, there is a considerable pressure drop in the pressure conduit region downstream of the displacer member of the pump, and also suspension of the delivery of the fuel.

In all three above-described operating conditions that gives rise to problems because, after a complete collapse in the delivery of fuel caused by the occurrence of gas bubbles, the fuel pump is capable only after some time, if at all, of automatically resuming the delivery of fuel.

Particularly in the heating mode, when the pump is not capable for a certain period of time of again building up and setting the required pressure, there is the danger that the fuel cone which is injected in the combustion chamber by the atomizer nozzle is modified so greatly or disappears completely so that combustion is stopped. Heating devices with electronic control devices then often lock out and for the time being a heating mode is no longer possible.

Hitherto, to overcome those problems, recourse was often had to external additional devices for automatically or autonomously venting the fuel which has been sucked in. Also, in relation to the fuel conduits, the system is switched over from two-line systems to one-line systems, which in part are in the form of a bypass between the return conduit and the suction conduit. In addition pre-delivery pumps are in part used, which again raise the level of the reduced pressure in the suction conduit.

A disadvantage with those remedial measures is that it is necessary to use additional components which markedly increase the manufacturing costs of such a system.

In comparison the object of the invention is to develop a heating device of the kind set forth in the opening part of this specification in such a way that gas bubbles which are sucked in with the fuel by the fuel pump do not lead to failure of the heating device or at least lead to such a failure much less frequently than in the state of the art.

To attain that object the invention provides the features recited in claim 1.

In the previous heating devices of the kind set forth in the opening part of this specification the endeavor was to minimize the volume of the pressure conduit region, that is to say between the displacer member of the pump and the fuel atomizer nozzle. On the one hand, the aim thereby was to achieve a structural size which was as small as possible and in addition the aim was to keep down post-drip of fuel from the atomizer nozzle, which under some circumstances occurs after termination of the heating mode of operation.

Thus for example in the gear pumps corresponding to the state of the art and which are specifically in use and which the applicant fits in vehicle heating appliances and systems which they manufacture and which are also marketed as replacement parts, both the pressure regulator and also the shut-down device and also the nozzle holder carrying the atomizer nozzle are integrated into the pump, thereby giving a very small volume in respect of the conduits connecting those units together.

Surprisingly it has now been found that, when the pressure conduit region between the displacer member of the pump and the atomizer nozzle and/or the pressure regulator is increased in size by at least one additional volume, the pressure drop which occurs on the pressure side when gas bubbles are sucked in by the fuel pump can be considerably reduced both in respect of the size thereof and also the time duration thereof, so that the probability of a complete shut-down of the heating device is considerably reduced.

When a shut-off device for interrupting the feed of fuel to the atomizer nozzle is provided in the pressure conduit region, the at least one additional volume providing for stabilization of the heating process is associated with the part of the pressure conduit region between the displacer member of the fuel pump, the shut-off device and the pressure regulator.

Alternatively it is possible to provide two additional volumes of which one is associated with the part of the pressure conduit region between the displacer member of the fuel pump, the shut-off device and the pressure regulator and the other is associated with the part of the pressure conduit region between the shut-off device and the atomizer nozzle. In that case it is possible to prevent unwanted post-drip by an emptying conduit which is provided with a controllable emptying valve and by means of which fuel which after termination of the heating mode is still to be found between the shut-off device and the atomizer nozzle can be returned to the supply container.

The additional volume or volumes can be associated with the respective part of the pressure conduit region either by conduit portions which are present in any case being increased in length and/or by their being increased in size in respect of their cross-section.

An alternative involves connecting pressure-side conduit portions which are short and of small cross-section by way of a branch conduit to a storage or supply chamber for the fuel which is under pressure.

According to the invention it is also possible to provide combinations of those various configurations of the additional volume or the plurality of additional volumes.

The size of the additional volume or volumes which is or are provided according to the invention and which is or are required to achieve the effect of the reduction in size and reduction in terms of time of a pressure drop, occurring when gas bubbles are sucked in, on the pressure side of the fuel pump, depends in the specific individual case on a series of factors like for example the fuel volume which is to be delivered per unit of time by the fuel pump in regular operation, the ratio of conduit volume on the suction side to that on the pressure side of the fuel pump, and so forth, but can readily be ascertained by the man skilled in the art by appropriate tests.

The invention is described hereinafter by means of embodiments by way of example with reference to the drawing in which:

FIG. 1 shows a diagrammatic view of a heating device according to the invention, in which the additional volumes are afforded by enlarging and/or increasing the length of conduit regions which are present in any case, and

FIG. 2 shows a diagrammatic view of a heating device according to the invention in which the additional volumes are in the form of additional storage chambers which are connected by branch conduits to the conduit regions which are present in any case.

In the Figures identical parts and components are denoted by the same references.

Both Figures show a fuel pump 1 whose displacer member 2 is driven by a motor 3 and which admittedly preferably involves a gear pump but which alternatively can also be any other type of pump. The motor 3 can be an independent unit in the manner illustrated or it can be integrated into the fuel pump 1.

The fuel pump 1 sucks fuel from a fuel tank 6 by way of a suction conduit 4, as indicated by the arrow S.

On the pressure side of the displacer member 2 of the fuel pump 1 there is firstly a conduit 7 which is internal to the pump, leading to a shut-off device which is in the form of a shut-off valve 8 and which is adjoined by a further conduit 9 which feeds the fuel to an atomizer nozzle 10 through which it is injected into a combustion chamber (not further shown) in order there to be burnt as a flame 11.

The shut-off valve 8 is actuable by way of a solenoid 12 and serves to be closed when no heating mode of operation is running.

The pressure which obtains in the conduits 7 and 9 and which in the above-mentioned pumps of the applicant can typically be in a range of between 9 and 10 bars is defined by an adjustable pressure regulator 14 which by way of a return conduit 16 returns the fuel which is delivered in excess by the fuel pump 1 back into the fuel tank 6, as indicated by the arrow R. Instead of that two-line system the return conduit 16, instead of communicating with the fuel tank 6, can open into the suction conduit 4 as is indicated by the dotted line 17 (one-line system). In that case the branch of the return conduit 16 which leads to the fuel tank 6, is omitted.

The minimum volume which is absolutely necessary for passing the fuel further from the displacer member 2 of the fuel pump 1 to the atomizer nozzle 10 and which is also present in the state of the art is indicated by the fact that the conduits 7 and 9 are shown in thin lines.

In addition in FIGS. 1 and 2 the shut-off valve 8, the solenoid 12 serving for actuation thereof and the pressure regulator are shown as units which are integrated in the fuel pump 1, that is to say which are assembled to the pump body, while the atomizer pump 10 which is generally mounted on a nozzle holder (not shown) is at a somewhat greater spacing from the fuel pump 1.

That arrangement however is not necessarily implemented; thus, individual ones, all or any combinations of the units 8, 12 or 14 can be positioned separately from the pump body. In that case then at least parts of the conduit 7 are external to the pump. On the other hand the nozzle holder can be assembled directly to the pump 2 so that the conduit 9 is then also a conduit which is internal to the pump. According to the invention it is also possible to provide any other variations and combinations of the possible arrangements just mentioned.

In each of those cases according to the invention beyond the minimum volume required for connecting all those component parts in flow relationship there is provided at least one additional volume 20, 22 which is associated with the parts of the pressure conduit region, that are disposed between the displacer member 2 of the fuel pump 1, the pressure regulator 14 and the shut-off valve 8 and/or between the shut-off valve 8 and the atomizer nozzle 10.

In the embodiment shown in FIG. 1 that association is such that the cross-section of the conduits 7 and 9 which are present in any case is increased in size either directly or by the provision of parallel conduits, as is indicated by rectangles shown in broken line, which surround those conduit portions 7 and 9. Each of those additional volumes 20, 22 can be provided either in itself alone or jointly with the respective other one.

In comparison FIG. 2 shows additional volumes 24, 26 which are connected to the conduits 7 and 9 respectively by way of branch conduits 27, 29 and thus are not disposed directly in the flow paths which lead from the displacer member 2 of the fuel pump 1 to the shut-off valve 8 or from there to the atomizer nozzle 10.

Depending on the respective specific aspects of the individual case those additional volumes 24, 26 can also be arranged internally of the pump and/or externally of the pump and can be combined in any fashion with the additional volumes 20, 22. The total size of the additional volume or volumes 20, 22, 24, 26 can preferably be more than 100 mm³, particularly preferably more than 200 mm³ and quite particularly preferably more than 400 mm³, or can be in a range of between 10% and 60%, particularly preferably between 20% and 50% and quite particularly preferably between 30% and 40% of the minimum required volume necessary for connecting the components disposed on the pressure side of the displacer member 2 of the fuel pump 1 in any case. 

1. A heating device operated with liquid fuel, comprising a fuel pump (1) which includes a displacer member (2) and serves to suck the liquid fuel out of a tank (6) and feed it to a pressure conduit region (7, 9) in which an increased pressure defined by a pressure regulator (14) prevails and which further passes the fuel to an atomizer nozzle (10) from which it passes into a combustion chamber to form a burner flame (11), wherein the pressure conduit region (7, 9) includes at least one additional volume (20, 22; 24, 26), the size of which is so selected that the pressure drop occurring in the pressure conduit region (7, 9) when gas bubbles are sucked in does not lead to a longer lasting interruption in the fuel delivery by the fuel pump (1).
 2. A heating device as set forth in claim 1 wherein provided between the displacer member (2) of the fuel pump (1) and the atomizer nozzle (10) is a shut-off valve (8) for interrupting the feed of fuel to the atomizer nozzle (10), wherein the additional volume (20; 24) is provided between the displacer member (2) of the fuel pump (1) and the shut-off valve (8).
 3. A heating device as set forth in claim 1 wherein provided between the displacer member (2) of the fuel pump (1) and the atomizer nozzle (10) is a shut-off valve (8) for interrupting the feed of fuel to the atomizer nozzle (10), wherein the additional volume (22; 26) is provided between the shut-off valve (8) and the atomizer nozzle (10).
 4. A heating device as set forth in claim 1, wherein at least a part of the additional volume (20, 22; 24, 26) is disposed in the interior of the fuel pump (1).
 5. A heating device as set forth in claim 1, wherein at least a part of the additional volume (24, 26) is in the form of a chamber which communicates with the pressure conduit region (7, 9) by way of a branch conduit (27, 29) and which is not arranged directly in the flow path leading from the displacer member (2) of the fuel pump (1) to the atomizer nozzle (10).
 6. A heating device as set forth in claim 1, wherein at least a part of the additional volume (20, 22) is in the form of an enlargement of conduits which are present in any case in the flow path leading from the displacer member (2) of the fuel pump (1) to the atomizer nozzle (10).
 7. A fuel pump (1) for a heating device as set forth in claim 1, wherein at least a part of the additional volume (20, 22; 24, 26) is arranged in the interior of the fuel pump (1).
 8. A fuel pump (1) as set forth in claim 7 wherein the fuel pump is a gear fuel pump (1).
 9. A fuel pump (1) as set forth in claim 7 which has a fuel pump cover (1) carrying a nozzle holder serving to hold the atomizer nozzle (10), wherein at least a part of the additional volume (20, 22; 24, 26) is provided in the fuel pump cover (1).
 10. A fuel pump (1) as set forth in claim 7, wherein at least a part of the additional volume (20, 22; 24, 26) is provided in the interior of the pump housing.
 11. A fuel pump (1) as set forth in claim 9 wherein at least a part of the additional volume (22; 26) is provided in the nozzle holder. 